Incidence and Predictive Factors of Distal Pedicle Screw Loosening Followed Posterior Corrective Surgery for Degenerative Lumbar Scoliosis

Abstract

BackgroundThe aim of this study was to identify the prevalence of distal pedicle screw loosening (DPSL) following posterior decompression and instrumented fusion for DLS, to search for predictable risk factors for DPSL, and hope to provide references in decision making and surgical planning for spine surgeons. MethodsOne hundred and fifty-three consecutive DLS patients surgically treated between January 2013 and July 2018 were retrospectively reviewed. The diagnostic criteria for DPSL developed by X-ray include the radiolucent area (thicker than 1 mm) around screw and the “double halo” sign defined as the presence of radiolucent area and radiopaque rim at the same X-ray. According to the occurrence of DPSL at two-year follow-up, patients were divided into two groups: study group (screw loosening) and control group (without screw loosening). To investigate predictive factors for distal pedicle screw loosening, three categorized factors were analyzed statistically.ResultsDPSL was detected in 72 of 153 patients (47.1%) at two-year follow up, and were enrolled as study group. Another 81 patients presented no screw loosening at two-year follow up, and were enrolled as control group. Hounsfield unit (HU) value was lower in study group than that in control group. Fusion level was longer in study group than that in control group. Lower instrumented vertebrae on L5 was less in study group than that in control group. Posterolateral fusion was less in study group than that in control group. Preoperative Cobb angle, postoperative Cobb angle, Cobb angle correction, preoperative lumbosacral coronal angle (LSCA), LSCA correction, preoperative thoracolumbar junction (TL), postoperative TL were larger in study group than those in control group. Logistic regression analysis revealed that low Bone mineral density (BMD) (<169 HU), posterolateral fusion, Cobb angle correction (>16 degrees), LSCA correction (>9 degrees) were independently associated with DPSL.ConclusionsThe incidence of DPSL following posterior decompression and instrumented fusion for DLS is 47.1%. Low BMD, large correction of both main curve and fractional curve are predictive factors for DPSL, while posterolateral fusion is a protective factor.